1. Field of the Invention
The present invention relates to a propulsion unit comprising a combined turborocket and ramjet with afterburner.
2. Summary of the Prior Art
Composite or combined propulsion units consisting of a turbojet and a ramjet are already known.
These systems put to good use the differing and complementary qualities of these two types of engine, the first of which is suited for propulsion at relatively low speeds, i.e. subsonic or supersonic speeds up to Mach 2.5 or 3, while the second enables highly supersonic or hypersonic speeds to be reached at the same time as providing good efficiency and low specific fuel consumption.
Engines are also known in which the turbine is not aerodynamically coupled to the compressor. This allows the input of energy to the turbine to be independent of the flow of air through the compressor, and also allows the use of a fuel which ensures efficient conversion of the energy into thrust during the process of expansion through the turbine.
French Patent 2 215 538 describes a combined turbojet-ramjet engine in which a direct-acting, hydrogen-expanding turbine drives an air compressor by means of a central shaft, the turbine being arranged in the central body of the propulsion unit and having means for ejecting the hydrogen thus expanded into the airstream where, mixed with the air, it will then be burnt. For high speeds, the hydrogen is introduced directly into the combustion chamber for ramjet operation and the turbine, which is no longer supplied, simply auto-rotates.
This device uses a cycle known as an expander cycle, in which the liquid hydrogen is heated to take up energy and then is used b expanding it in the turbine before being burned in the airstream.
U.S. Pat. No. 3,237,400 discloses a turborocket propulsion unit with reheat in which the combustion gases of a central rocket motor drive the turbine and also, by means of a reduction gear, a compressor placed upstream. Such an arrangement is also described in Flight International, Vol. 86, No 2903 (pp 752 to 754) of Oct. 29, 1964.